Aqueous dispersion of vinylidene fluoride polymer and preparation process therof

ABSTRACT

Aqueous dispersion of a vinylidene fluoride (VdF) polymer which comprises a VdF polymer having a particle size of not more than 200 nm and contains 30 to 50% by weight of solids and not more than 1% by weight of a fluorine-containing surfactant on the basis of water. This aqueous dispersion is prepared by emulsion-polymerizing VdF monomer or a monomer mixture containing VdF under coexistence of not more than 1% by weight of the fluorine-containing surfactant and 0.001 to 0.1% by weight of a nonionic non-fluorine-containing surfactant on the basis of water, and is suitably used for paints.

TECHNICAL FIELD

[0001] The present invention relates to an aqueous dispersion of afluorine-containing polymer usable for paints. More specifically thepresent invention relates to an aqueous dispersion of a vinylidenefluoride (VdF) type polymer, which comprises a VdF polymer having aparticle size of not more than 200 nm and contains 30 to 50% by weightof solids, and a process for preparation thereof.

BACKGROUND ART

[0002] Fluorine-containing paints are used as weather resistive paintsfor exterior and interior coating of medium- or low-storied buildings,and various techniques have been developed for preparation of thefluorine-containing paints. Though many of the fluorine-containingpaints are in the form of organic solvent dispersions, there areproblems in the use of organic solvents from safety and environmentalprotection points of view, and ones of aqueous dispersion type arepreferable. As the methods of preparing an aqueous dispersion of afluorine-containing polymer, there are known the methods mentionedbelow.

[0003] For example, JP-B-28669/1974 discloses that when vinyl fluorideis suspension-polymerized in preparation of paints, a nonionicsurfactant is added in an amount of 0.05 to 5% by weight on the basis ofthe monomer to increase yield, to prevent deposition of the polymer ontoan inside wall of a polymerization tank and to control particle size ofthe polymer.

[0004] Also JP-A-123646/1986 discloses that in preparing afluorine-containing copolymer in an aqueous medium, a stable aqueousemulsion can be obtained by adding a dispersion stabilizing agent afterpolymerization of the fluorine-containing copolymer, but before orduring the condensation process of the aqueous dispersion.

[0005] Further JP-B-55441/1992 discloses that in preparing an aqueousfluorine-containing polymer dispersion for aqueous paints, 0.05 to 5.0%by weight of surfactants of various kinds including a nonionicsurfactant is added when the seed-polymerization of a monomer havingethylenically unsaturated bond is carried out.

[0006] Also JP-A-225550/1990 discloses that a mixture of afluorine-containing type surfactant and a nonionic type surfactant isused when copolymerizing a fluorine-containing olefin and a hydrophilicgroup-containing non-fluorine-containing olefin.

[0007] Also Koubunshi Ronbun Shu, Vol. 36, No. 11 (1979) discloses atpages 729 to 737 that when a large amount of surfactants of variouskinds is used in emulsion polymerization, particles of a polymer latexbecome smaller, and also that by mixing an anion surfactant and a nonionsurfactant in polymerization of an acrylic monomer, there can beobtained the same effect as in case of adding an anion surfactantsolely.

[0008] However the technique in JP-B-28669/1974 does not relate toemulsion polymerization, but relates to suspension polymerizationwithout using a fluorine-containing surfactant, and intends to obtain aparticle size larger than that of the present invention. The particlesize described in Example of this patent publication is as large as 3.4to 4.5 μm .

[0009] Also JP-A-123646/1986 discloses that a polymer latex having aconcentration as high as not less than 30% by weight is obtained byusing a fluorine-containing emulsifying agent in polymerization process.However there is no description as to the use of a fluorine-containingsurfactant for controlling the particles at a size lower than a certainsize. In addition, the invention is characterized by the use of aspecific non-fluorine-containing dispersion stabilizing agent, and itsamount to be used is as much as 2 to 8% by weight on the basis of asolid content. Usually the particle size of a latex tends to increasetogether with a polymer concentration, and when the fluorine-containingsurfactant is used solely and if its amount is not more than 1% byweight, there cannot be obtained a particle size of not more than 200 nmif the solid content is assumed to be 30 to 50% by weight. Also there isno description as to controlling of the particle size of the aqueouslatex. It is also described that if the nonionic surfactant is added inpreparing an aqueous emulsion, there is an adverse effect such ascoloring.

[0010] Further in the technique disclosed in JP-B-55441/1992, nosurfactant is used in the polymerization of a fluorine-containingolefin, and also there is no disclosure as to the use of afluorine-containing surfactant as the surfactant to be used in theseed-polymerization.

[0011] Also the technique specifically disclosed in JP-A-225550/1990 isone wherein chlorotrifluoroethylene is used as a fluoroolefin unit andthe amount of the nonionic surfactant used is as relatively much as 3%by weight on the basis of water. However in copolymerization of VdF,there has been generally known that there occur problems such that whenthe nonionic surfactant is added, the reaction rate is loweredremarkably and the molecular weight is not increased.

[0012] Also in the techniques disclosed in the above-mentioned KoubunshiRonbun Shu, the use of the surfactant in a large amount causes anadverse effect on water resistance when used for paints.

[0013] The present invention has been made to solve the above-mentionedproblems, and it is an object of the present invention to provide anaqueous dispersion of a fluorine-containing polymer, which comprises aVdF polymer having a particle size as small as not more than 200 nm andcontains solids in an amount as high as 30 to 50% by weight and asurfactant in an amount as low as not more than 1% by weight on thebasis of water, and its preparation process.

DISCLOSURE OF THE INVENTION

[0014] The present invention relates to an aqueous dispersion of a VdFpolymer, which comprises a VdF polymer having a particle size of notmore than 200 nm, has a solid content of 30 to 50% by weight andcontains a fluorine-containing surfactant in an amount of not more than1% by weight on the basis of water.

[0015] It is possible in the present invention that in the knownemulsion polymerization system, notwithstanding that the solid contentis as high as 30 to 50% by weight, the particle size can be decreased tonot more than 200 nm by adding a nonionic non-fluorine-containingsurfactant in a trace amount of 0.001 to 0.1% by weight on the basis ofwater in the presence of a small amount of a fluorine-containingsurfactant, i.e. not more than 1% by weight, on the basis of water.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] As the VdF polymer in the present invention, there arehomopolymer of VdF; a copolymer of VdF monomer and at least one of theother fluorine-containing monomers such as tetrafluoroethylene (TFE),trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE) andhexafluoropropylene (HFP); a copolymer of VdF, the otherfluorine-containing monomer and a monomer having an unsaturated bondwhich is copolymerizable therewith. The preferable copolymers are, forexample, VdF/TFE copolymer, VdF/TFE/HFP copolymer, VdF/TFE/CTFEcopolymer, VdF/TFE/TrFE copolymer, VdF/CTFE copolymer, VdF/HFPcopolymer, VdF/TFE/HFP/CTFE copolymer, VdF/TFE/perfluorobutenoic acidcopolymer, VdF/TFE/maleic acid copolymer and the like. The content ofVdF units of these copolymers is preferably not less than 50% by mole,more preferably not less than 70% by mole. The weight average molecularweight (Mw) of these VdF polymers is from 1,000 to 1,000,000, preferablyfrom 10,000 to 500,000. When lower than 1,000, mechanical properties andweatherability when forming a film tend to be inferior, and when higherthan 1,000,000, there are tendencies that the resin does not flow whenforming a film, leveling property is lowered and no gloss is exhibited.

[0017] The particle size of the VdF polymer is not more than 200 nm,preferably from 150 to 100 nm. Since the particle size is as small asnot more than 200 nm, the polymer is excellent in stability againstsedimentation and dispersing property of additives is excellent. Whenthe particle size is larger than 200 nm, there occurs sedimentation andcoagulation of the particles during storage of the dispersion and thedispersing property of the additives is poor. Also there is a tendencythat gloss of the formed film is difficult to be obtained.

[0018] The fluorine-containing surfactant used in the present inventionis one or a mixture of compounds containing fluorine atoms in theirstructures and having surface activity. For example, there are an acidrepresented by X(CF₂)_(n)COOH (n is an integer of 6 to 20, X is F or H),its alkali metal salt, ammonium salt, amine salt or quaternary ammoniumsalt; an acid represented by Y(CH₂CF₂)_(m)COOH (m is an integer of 6 to13, Y is F or Cl), its alkali metal salt, ammonium salt, amine salt orquaternary ammonium salt; or the like. More specifically there are usedan ammonium salt of perfluoro(octanoic acid), an ammonium salt ofperfluoro(nonanoic acid) or the like. In addition, there can be usedknown fluorine-containing surfactants.

[0019] The amount of the fluorine-containing surfactant to be used isnot more than 1.0% by weight on the basis of water, preferably not morethan 0.5% by weight, more preferably not more than 0.2% by weight. Thelower limit is usually 0.01% by weight. When more than 1.0% by weight,there occurs a phenomenon such as precipitation of the surfactant in thefilm formed from the aqueous dispersion and also there is a tendencysuch that water absorption increases to make the dispersion whiten. Thusit is not preferable if the amount of the fluorine-containing surfactantis more than 1.0% by weight.

[0020] The solid content of the aqueous dispersion of the presentinvention is from 30 to 50% by weight, preferably from 35 to 45% byweight. When less than 30% by weight, there is a tendency such that whenforming a film, viscosity adjustment is difficult and leveling propertyis lowered. When more than 50%, stability of the dispersion becomesworse, and deposition and coagulation tend to occur in polymerizationprocess.

[0021] Water to be used for an aqueous dispersion of the presentinvention is preferably a deionized water.

[0022] The aqueous dispersion of the VdF polymer of the presentinvention can be prepared, for example, by emulsion-polymerizing VdFmonomer or a monomer mixture containing VdF under coexistence of theabove-mentioned fluorine-containing surfactant in an amount of not morethan 1% by weight on the basis of water and a trace amount of thenonionic non-fluorine-containing surfactant.

[0023] In order to prepare the aqueous dispersion which comprises theVdF polymer having a particle size of not more than 200 μm and containssolids in an amount of 30 to 50% by weight, it is usually necessary touse a large amount of a fluorine-containing surfactant. Howeveraccording to the preparation process of the present invention, it ispossible to decrease the amount of the fluorine-containing surfactant toa small amount of not more than 1% by weight by adding a trace amount ofthe nonionic non-fluorine-containing surfactant. Namely, a smallparticle size of not more than 200 nm can be attained by adding thenonionic non-fluorine-containing surfactant.

[0024] As the nonionic non-fluorine-containing surfactant, there arepolyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers,polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylenesorbitan alkyl esters, glycerol esters, their derivatives and the like.More specifically examples of polyoxyethylene alkyl ethers arepolyoxyethylene lauryl ether, polyoxyethylene cetyl ether,polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,polyoxyethylene behenyl ether and the like; examples of polyoxyethylenealkyl phenyl ethers are polyoxyethylene nonyl phenyl ether,polyoxyethylene octyl phenyl ether and the like; examples ofpolyoxyethylene alkyl esters are polyethylene glycol monolaurylate,polyethylene glycol monooleate, polyethylene glycol monostearate and thelike; examples of sorbitan alkyl esters are polyoxyethylene sorbitanmonolaurylate, polyoxyethylene sorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan monooleate and the like;examples of polyoxyethylene sorbitan alkyl esters are polyoxyethylenesorbitan monolaurylate, polyoxyethylene sorbitan monopalmitate,polyoxyethylene sorbitan monostearate and the like; and examples ofglycerol esters are glycerol monomyristate, glycerol monostearate,glycerol monooleate and the like. Also examples of their derivatives arepolyoxyethylene alkyl amine, polyoxyethylene alkyl phenyl-formaldehydecondensate, polyoxyethylene alkyl ether phosphate and the like.Particularly preferable are polyoxyethylene alkyl ethers andpolyoxyethylene alkyl esters which have an HLB value of 10 to 18. Moreparticularly there are polyoxyethylene lauryl ether (EO: 5 to 20. EOstands for an ethylene oxide unit.), polyethylene glycol monostearate(EO: 10 to 55) and polyethylene glycol monooleate (EO: 6 to 10).

[0025] The amount of the nonionic non-fluorine-containing surfactantused in the present invention is from 0.001 to 0.1% by weight on thebasis of water, preferably from 0.01 to 0.05% by weight. When more than0.1% by weight, it is not practicable because the rate of reaction islowered because of chain transfer reaction and the reaction is stopped.Also when less than 0.001% by weight, there is almost no effect ofmaking the particle size fine.

[0026] The emulsion having a relatively high concentration can also beobtained by polymerizing, in an organic solvent, a monomer mixturecontaining an ethylenically unsaturated monomer having an ionic group orpolyalkylene oxide group, then adding water and distilling off theorganic solvent. For example, an emulsion can be obtained bysolution-polymerizing, in ethyl acetate, a mixture of VdF, TFE andperfluorobutenoic acid (CF₂=CF—F₂COOH), adding aqueous ammonia solutionto neutralize, then pouring dropwise into ion-exchanged water containinga fluorine-containing surfactant with stirring to dispersehomogeneously, and distilling off ethyl acetate by using an evaporator.

[0027] In order to polymerize VdF monomer, an initiator is usually used.As the initiator, particularly there is no restriction if it serves togenerate radicals usable for free radical reaction in an aqueous mediumat a temperature between 20° C. and 90° C. Usually as the water solubleinitiator, there are potassium salt and ammonium salt of persulfuricacid, and hydrogen peroxide; and as the oil soluble initiator, there arediisopropyl peroxydicarbonate (IPP), azobisisobutyronitrile (AIBN) andthe like. The amount of the initiator to be added is from 0.005 to 1.0%by weight on the basis of water, preferably from 0.01 to 0.5% by weight.When less than 0.005% by weight, the polymerization rate tends to belowered extremely, and when more than 1.0% by weight, there is atendency such that a concentration of an electrolyte is increased andthus the particle size is increased.

[0028] In preparing the aqueous dispersion of the VdF polymer of thepresent invention, the polymerization temperature is from 20° to 120°C., preferably from 30° to 70° C. When lower than 20° C., in generalthere is a tendency such that stability of the formed latex is lowered,and when higher than 120° C., the polymerization rate tends to bedecreased due to chain transfer reaction. Polymerization is usuallycarried out by heating for 5 to 100 hours under a pressure of 1.0 to 50kgf/cm² (gauge pressure) though it depends on kind of the polymer.

[0029] The aqueous dispersion of the VdF polymer of the presentinvention can be used as water base paints for coating by blendingadditives such as pigments, thickeners, dispersing agents, defoamingagents, antifreezing agents and film forming auxiliaries or in additionthereto by combining with other high molecular compounds.

[0030] The present invention is explained further in detail based onexamples, but is not limited thereto.

EXAMPLE 1

[0031] A one-liter pressure resistive reactor equipped with a stirrerwas charged with 500 ml of deionized water, 0.5 g of afluorine-containing surfactant, i.e. an ammonium salt ofperfluoro(octanoic acid) (PFOA) and 0.05 g of a nonionicnon-fluorine-containing surfactant, i.e. polyoxyethylene lauryl ether(MYS40 available from Nikko Chemicals Co., Ltd.), and steps ofintroduction of pressurized nitrogen gas and deaeration were repeated toremove the dissolved air. The inside pressure of the reactor was thenraised to 20 kgf/cm² (gauge pressure) at 60° C. by using VdF. Then 0.2 gof an initiator, i.e. ammonium persulfate was added, VdF wascontinuously supplied to maintain the inside pressure of the reactorconstant at 20 kgf/cm² (gauge pressure), and the reaction was carriedout for 20 hours. Afterwards the reaction system was rendered to normaltemperature and normal pressure, and thereby the reaction wasterminated. The intrinsic viscosity [η] of the obtained polymercomprising VdF solely, which was measured in a dimethylfuran (DMF)solvent at 35° C., was 0.63. The measured characteristic values of theobtained aqueous dispersion are shown in TABLE 1.

[0032] In TABLE 1, the solid content is represented in percentage of theweight of the aqueous dispersion after dried at 150° C. for one hour ina vacuum dryer to its weight before drying. The particle size is anaverage size obtained by measuring the particle sizes with a laser beamscattering particle size analyzer (ELS-3000 available from Otsuka DenshiKogyo Kabushiki Kaisha). The stability against sedimentation wasevaluated as follows by allowing an aqueous dispersion to be tested tostand at 25° C. for 60 days.

[0033] ◯: There is no change in dispersed state with naked eyes.

[0034] Δ: The dispersion is separated into a transparent water phase anda dispersed particle phase and it is possible to re-disperse by shaking.

[0035] X: The dispersion is separated into a transparent water phase anda dispersed particle phase, and it is impossible to re-disperse byshaking.

EXAMPLE 2

[0036] A one-liter pressure resistive reactor equipped with a stirrerwas charged with 500 ml of deionized water, 0.5 g of an ammonium salt ofperfluoro(octanoic acid) and 0.05 g of polyoxyethylene lauryl ether, andsteps of introduction of pressurized nitrogen gas and deaeration wererepeated to remove the dissolved air. The inside pressure of the reactorwas then raised to 8 kgf/cm² (gauge pressure) at 60° C. by using aVdF/TFE monomer mixture (80/20% by mole). Then 0.05 g of ammoniumpersulfate was added, the above-mentioned monomer mixture wascontinuously supplied to maintain the inside pressure of the reactorconstant at 8 kgf/cm² (gauge pressure), and the reaction was carried outfor 20 hours. Afterwards the reaction system was rendered to normaltemperature and normal pressure, and thereby the reaction wasterminated. The intrinsic viscosity [η] of the obtained VdF/TFEcopolymer in a methyl ethyl ketone (MEK) solution at 35° C. was 1.43.The measured characteristic values of the obtained aqueous dispersionare shown in TABLE 1.

EXAMPLE 3

[0037] A one-liter pressure resistive reactor equipped with a stirrerwas charged with 500 ml of deionized water, 0.5 g of an ammonium salt ofperfluoro(octanoic acid) and 0.05 g of polyoxyethylene lauryl ether, andsteps of introduction of pressurized nitrogen gas and deaeration wererepeated to remove the dissolved air. The inside pressure of the reactorwas then raised to 8 kgf/cm² (gauge pressure) at 60° C. by using aVdF/TFE/HFP monomer mixture (72/20/8% by mole). Then 0.2 g of ammoniumpersulfate was added, the above-mentioned monomer mixture wascontinuously supplied to maintain the inside pressure of the reactorconstant at 8 kgf/cm² (gauge pressure), and the reaction was carried outfor 38 hours. Afterwards the reaction system was rendered to normaltemperature and normal pressure, and thereby the reaction wasterminated. The intrinsic viscosity [η] of the obtained VdF/TFE/HFPcopolymer in an MEK solvent at 35° C. was 1.08. The measuredcharacteristic values of the obtained aqueous dispersion are shown inTABLE 1.

EXAMPLE 4

[0038] A one-liter pressure resistive reactor equipped with a stirrerwas charged with 500 ml of deionized water, 0.5 g of an ammonium salt ofperfluoro(octanoic acid) and 0.05 g of polyoxyethylene lauryl ether, andsteps of introduction of pressurized nitrogen gas and deaeration wererepeated to remove the dissolved air. The inside pressure of the reactorwas raised to 8 kgf/cm² (gauge pressure) at 60° C. by using aVdF/TFE/CTFE monomer mixture (75/15/10% by mole). Then 0.2 g of ammoniumpersulfate was added, the above-mentioned monomer mixture wascontinuously supplied to maintain the inside pressure of the reactorconstant at 8 kgf/cm² (gauge pressure), and the reaction was carried outfor 40 hours. Afterwards . the reaction system was rendered to normaltemperature and normal pressure, and thereby the reaction wasterminated. The intrinsic viscosity [η] of the obtained VdF/TFE/CTFEcopolymer in an MEK solvent at 35° C. was 1.20. The measuredcharacteristic values of the obtained aqueous dispersion are shown inTABLE 1.

COMPARATIVE EXAMPLES 1 TO 4

[0039] Aqueous dispersions of the VdF polymer were prepared in the samemanner as in EXAMPLES 1 to 4 except that the nonionicnon-fluorine-containing surfactant was not used and the amount of thefluorine-containing surfactant was changed as shown in TABLE 1. Themeasured characteristic values of the obtained aqueous dispersions areshown in TABLE 1.

COMPARATIVE EXAMPLE 5

[0040] An aqueous dispersion of the VdF polymer was prepared in the samemanner as in EXAMPLE 3 except that CTFE was used instead of HFP and theamount of the fluorine-containing surfactant was changed as shown inTABLE 1. The measured characteristic values of the obtained aqueousdispersion are shown in TABLE 1. As shown in TABLE 1, thesecharacteristics were preferable, but there was found precipitation ofthe fluorine-containing surfactant at drying the formed film TABLE 1Com. Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4Ex. 5 Monomer VdF*¹ 100 80 72 75 100 80 72 75 72 (% by mole) TFE*² — 2020 15 — 20 20 15 20 HFP*³ — — 8 — — — 8 — — CTFE*⁴ — — — 10 — — — 10 8Surfactant Fluorine- PFOA*⁵ PFOA PFOA PFOA PFOA PFOA PFOA PFOA PFOA (%by weight) containing (0.1) (0.1) (0.1) (0.1) (1.0) (1.0) (1.0) (0.1)(2.0) type Nononic MYS40*⁶ MYS40 MYS40 MYS40 — — — — — non-fluorine-(0.01) (0.01) (0.01) (0.01) (0.01) containing type Aqueous Solid content30.1 32.1 33.4 42.0 18.5 24.6 32.0 34.6 31.5 dispersion (% by weight)Particle size 180.5 167.3 125.9 165.0 231.7 269.2 234.5 320.1 196.3 (nm)Stability against ∘ ∘ ∘ ∘ Δ x x x ∘ sedimentation

INDUSTRIAL APPLICABILITY

[0041] The aqueous dispersion of the VdF polymer of the presentinvention is excellent in stability against sedimentationnotwithstanding a small amount of a surfactant and can provide coatingfilms excellent in water resistance and leveling property. According tothe preparation process of the present invention, the above-mentionedaqueous dispersion can be prepared easily by using a trace amount of anonionic non-fluorine-containing surfactant even if the amount of afluorine-containing surfactant is decreased greatly.

1. An aqueous dispersion of a vinylidene fluoride polymer, whichcomprises a vinylidene fluoride polymer having a particle size of notmore than 200 nm, wherein a solid content is from 30 to 50% by weightand a content of a fluorine-containing surfactant is not more than 1% byweight on the basis of water.
 2. The aqueous dispersion of thevinylidene fluoride polymer of claim 1 , which contains 0.001 to 0.1% byweight of a nonionic non-fluorine-containing surfactant on the basis ofwater.
 3. A process for preparing the aqueous dispersion of thevinylidene fluoride polymer of claim 1 or 2 , wherein vinylidenefluoride monomer or a monomer mixture containing vinylidene fluoride isemulsion-polymerized under coexistence of not more than 1% by weight ofa fluorine-containing surfactant on the basis of water and 0.001 to 0.1%by weight of a nonionic non-fluorine-containing surfactant on the basisof water.